It depends how your Subsystems are setup. Allocation of users is not possible you will need to configure your session name so that it gets allocated to subsystem QCTL. In the subsystem descriptions you have a section "Work Station Name" entries and one "Workstation type entries". You also have the "Control Job At" for each entry. *SIGNON means that the subsystem will try to allocate the workstation as soon as it starts. *ENTER means that you can Transfer your job to the subsystem. One solution would be to have a workstation name entry in QCTL that is controlled at *SIGNON and the same entry in QINTER that is controlled at *ENTER. This works as a kind of "Exclude" entry. Otherwise there is no sure way to predict which subsystem allocates your workstation.